STM32F103C8T6使用ADC采集电压时，数据几乎始终保持最高值是为什么？

使用STM32F103C8T6 的PA0引脚为ADC采集脚位，一个10K的电位器输出电压。附上程序AD.c
#include "stm32f10x.h"                // Device header

void AD_Init(void){
      RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1,ENABLE);
      RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);

      RCC_ADCCLKConfig(RCC_PCLK2_Div6);

      GPIO_InitTypeDef GPIO_InitStructure;
      GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
      GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
      GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
      GPIO_Init(GPIOA,  GPIO_InitStructure);

      ADC_RegularChannelConfig(ADC1,ADC_Channel_0,1,ADC_Sampletime_55Cycles5);

      ADC_InitTypeDef ADC_InitStructure;
      ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;
      ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
      ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None;
      ADC_InitStructure.ADC_Mode = ADC_Mode_Independent;
      ADC_InitStructure.ADC_NbrOfChannel = 1;
      ADC_InitStructure.ADC_ScanConvMode = DISABLE;
      ADC_Init(ADC1, ADC_InitStructure);

      ADC_Cmd(ADC1,ENABLE);

      ADC_ResetCalibration(ADC1);
      while(ADC_GetResetCalibrationStatus(ADC1) == SET);
      ADC_StartCalibration(ADC1);
      while(ADC_GetCalibrationStatus(ADC1) == SET);

}
uint16_t AD_GetValue(void){
      ADC_SoftwareStartConvCmd(ADC1,ENABLE);
      while(ADC_GetFlagStatus(ADC1,ADC_FLAG_EOC)== RESET);
      return ADC_GetConversionValue(ADC1);

}
还不知哪里有问题，请各位大佬指教一下。感谢！